This invention relates to marine propellers, and more particularly, to a foldable marine propeller assembly.
Foldable marine propellers which employ a pair of pivotally mounted blades that move between a trailing, collapsed position and an outflung drive position are known. Such foldable marine propellers are commonly connected to a drive shaft by a shear pin to avoid damage to the drive shaft should excessive torque forces be developed. Representative prior art constructions of foldable propellers are disclosed in the following U.S. patents:
Learnard, U.S. Pat. No. 725,097--Apr. 14, 1903 PA1 Godfrey, U.S. Pat. No. 2,608,257--Aug. 26, 1952 PA1 Beck, U.S. Pat. No. 3,255,826--June 14, 1966 PA1 Butler, U.S. Pat. No. 3,591,311--July 6, 1971 PA1 Lorenz, U.S. Pat. No. 3,709,634--Jan. 9, 1973 PA1 Kettner, U.S. Pat. No. 3,715,171--Feb. 6, 1973 PA1 Ehrenskjold et al, U.S. Pat. No. 3,981,613--Sept. 21, 1976 PA1 Beck, U.S. Pat. No. 3,982,853--Sept. 28, 1976
The abrupt opening of the foldable propeller blades to the operative position can in itself create reactive torque forces that are sufficiently large to fracture the shear pin. None of the above patents discloses a means for absorbing this reactive force to lessen the chance of fracturing the shear pin under these circumstances.